# Quantum nanoconstrictions fabricated by cryo-etching in encapsulated graphene

## TL;DR

This paper presents a novel cryo-etching technique to fabricate high-quality graphene nanoconstrictions with smooth edges, enabling the observation of ballistic transport and quantized conductance steps consistent with theoretical predictions.

## Contribution

The study introduces an advanced cryo-etching method for creating graphene nanoconstrictions with unprecedented edge smoothness, facilitating ballistic transport and quantized conductance measurements.

## Key findings

- Observation of well-developed conductance quantization steps at 2e^2/h.
- Correlation between low edge roughness and ballistic transport.
- Successful fabrication of encapsulated graphene nanoconstrictions with atomic-scale edge control.

## Abstract

More than a decade after the discovery of graphene, ballistic transport in nanostructures based on this intriguing material still represents a challenging field of research in two-dimensional electronics. The presence of rough edges in nanostructures based on this material prevents the appearance of truly ballistic electron transport as theo\-re\-tically predicted and, therefore, not well-developed plateaus of conductance have been revealed to date. In this work we report on a novel implementation of the cryo-etching method, which enabled us to fabricate graphene nanoconstrictions encapsulated between hexagonal boron nitride thin films with unprecedented control of the structure edges. High quality smooth nanometer-rough edges are characterized by atomic force microscopy and a clear correlation between low roughness and the existence of well-developed quantized conductance steps with the concomitant occurrence of ballistic transport is found at low temperature. In par\-ti\-cu\-lar, we come upon exact 2$e^{2}/h$ quantization steps of conductance at zero magnetic field due to size quantization, as it has been theoretically predicted for truly ballistic electron transport through graphene nanoconstrictions.